1. Field of the Invention
The present invention relates to an in-plane switching (IPS) mode liquid crystal display (LCD) device, and more particularly, to an IPS mode LCD device and a fabrication method thereof having a high aperture ratio and improving a uniformity of common voltage distribution through all the display panel.
2. Discussion of the Related Art
With a development of an information-oriented society, needs for various flat panel displays improving defects of a conventional Cathode Ray Tube (CRT) such as heavy weight and large volume have increased.
To this, various flat panel displays such as Liquid Crystal Display (LCD) device, Organic Light Emitting Diode (OLED), Plasma Display Panel (PDP) Device, and Surface-conduction Electron-emitter Display (SED) Device have lately attracted attention.
Especially, an LCD device is representative one of them applied to a large-sized TV screen through a small-sized mobile phone screen.
Generally, LCD device uses an optical anisotropic property and polarization properties of liquid crystal (LC) molecules to display images. The LC molecules have orientation characteristics resulted from their thin and long shape. Accordingly, the arrangement of liquid crystal molecules, and their directions may be controlled by applying an electrical field to them.
Therefore, when the electrical field is applied to the LC molecules, the polarization properties of light are changed based on the arrangement of the LC molecules, which enables an LCD device to display images. According to a direction of electric field driving LC molecules, the LCD device is classified into a vertical electric field type LCD and a horizontal electric field type LCD.
In the vertical electric field type LCD, for example Twisted Nematic (TN) mode, LC molecules are driven by vertical electric field generated between a common electrode and a pixel electrode, because the common electrode is formed on an upper substrate and the pixel electrode is formed on a lower substrate. The vertical electric field type LCD has a large aperture ratio, but it has a defect of a narrow viewing angle of about 90°.
In the horizontal electric field type LCD, for example In-Plane Switching (IPS) mode, LC molecules are driven by horizontal electric field generated between a common electrode and a pixel electrode, because the common electrode and the pixel electrode are formed on the same substrate. The horizontal electric field type LCD has a wider viewing angle of 160° than the vertical electric field type LCD.
Hereinafter, a conventional in-plane switching mode LCD will be explained more circumstantially. A conventional in-plane switching mode LCD comprises a lower substrate and an upper substrate located at a predetermined interval, a spacer to maintain a fixed cell gap between the two substrates, and liquid crystal interposed between the two substrates.
A thin film transistor array (TFT array) and an alignment film layer applied to the TFT array for alignment of liquid crystal are formed on the lower substrate. The thin film transistor array includes a gate line, a data line crossed the gate line to define a pixel region, a thin film transistor (TFT) formed adjacent to a crossing of the gate line and the data line, and a pixel electrode connected to the TFT.
A color filter array (CF array) and an alignment film layer applied to the CF array for alignment of liquid crystal to are formed on the upper substrate. The CF array includes a black matrix formed as a shape of a matrix to define a pixel region and to shield light, and a color filter formed at the pixel region.
FIG. 1 is a plain view of the conventional LCD. As shown in FIG. 1, a lower substrate 45 in the conventional LCD includes a gate line, a gate insulating film 44 formed to cover the gate line, a data line 4 formed on the gate insulating film crossing the gate line to define a pixel region, a TFT formed adjacent to a crossing of the gate line and the data line, a passivation layer 50 formed to cover the TFT, a pixel electrode 14 formed on the passivation layer to be connected with the TFT, a common electrode 18 to generate a horizontal electric field with the pixel electrode, and a common line 16 formed in the pixel region to supply common voltage to the common electrode.
Under the data line 4, a semiconductor pattern 48 comprising an active layer 15 and an ohmic contact layer 49 can be formed.
The upper substrate 65 includes a black matrix 66 formed as a shape of a matrix to define a pixel region and to shield light, and a color filter 67 formed at the pixel region.
FIG. 1 is a perspective view of a related art LCD device. As shown in FIG. 1, the prior art LCD device includes a first substrate 1a, a second substrate 1b, and a liquid crystal layer 3. At this time, the first and second substrates 1a and 1b are bonded to each other at a predetermined interval, and the liquid crystal layer 3 is formed between the first and second substrates 1a and 1b by injection of liquid crystal.
However, the conventional in-plane switching mode LCD has a problem of low aperture ratio caused by several patterns formed in the pixel region such as the pixel electrode, the common electrode, and a common line to supply common voltage to the common electrode.
Additionally, after-image may be generated because a distribution of common voltage level through an entire display panel is non-uniformed owing to the line resistance.